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ENVISAT first quality assessment Calibration and cross-calibration. F-PAC activities

ENVISAT first quality assessment Calibration and cross-calibration. F-PAC activities Joël DORANDEU , Yannice FAUGERE , Françoise MERTZ - CLS , France. OUTLINE: Calibration / Validation, performance assessment Cross-calibration wrt ERS-2 and Jason-1.

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ENVISAT first quality assessment Calibration and cross-calibration. F-PAC activities

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  1. ENVISAT first quality assessment Calibration and cross-calibration. F-PAC activities Joël DORANDEU, Yannice FAUGERE, Françoise MERTZ- CLS, France OUTLINE: Calibration / Validation, performance assessment Cross-calibration wrt ERS-2 and Jason-1

  2. Calibration and cross-calibration. F-PAC activities • Objectives: • Quality assessment of ENVISAT data • Long-term monitoring of altimeter/radiometer parameters and geophysical corrections • Algorithm assessment and improvement • Cross-calibration with other altimeters/radiometers • Activation: • routinely in an operational context • particular investigations • long term monitoring • Tools : CMA/Verification tools and other CalVal tools • Connexions: • with ground segment teams • with other studies: SSB, MWR, in-situ measurements Quality assessment report: Associated to data dissemination

  3. Calibration and cross-calibration. F-PAC activities • ENVISAT data. Verification strategy: • to estimate the product data quality (GDR). • to assess/propose improvements. Product update: • Ice flag • Bent model ionosphere correction • GIM ionosphere correction • Along-track filtering of dual-frequency iono. • Correction of Sigma0 atmospheric attenuation • Radiometer correction (+1 dB Sigma0) • SSB estimation • CLS01 MSS model

  4. ENVISAT Calibration / Validation Joël DORANDEU, Yannice FAUGERE, Françoise MERTZ- CLS, France Data processing Altimeter parameter Radiometer parameter Envisat performances

  5. Available data - 3 cycles of GDR (10, 11, a part of 12) - Global coverage of 75% on cycle 10 and 11 - Missing measurements on cycle 11:

  6. S BandAnomal Mean /pass of Range Ku – Range S (m) (cycle 12)

  7. Main editing parameters Radiometer Land flag Ice flag -10 m < SSH – MSS < 10 m Number of 18 Hz measurements > 10 RMS of 18 Hz measurements < 20 cm -0.20 deg2 < Off-nadir angle < 0.16 deg2 0 < Ku SWH < 11 m 7 < Ku Sigma0 < 30 dB Other selections on geophysical corrections Selection of valid periods for S-band estimations

  8. Data selection

  9. Data selection

  10. Altimeter parameters RMS of elementary measurements RMS of Ku-Band Range (cm) RMS of S-Band Range (cm)

  11. Altimeter parameters RMS of elementary measurements RMS of S Range / RMS of Ku Range RMS of Ku Range / SWH

  12. Altimeter parameters Off-nadir angle (from waveforms) Mean /pass of Off-nadir angle (deg2) (cycle 10, 11, 12)

  13. Altimeter parameters Significant Wave Height SWH Ku SWH S

  14. Altimeter parameters Backscatter coefficient Sigm0 Ku Sigm0 S

  15. Altimeter parameters Ionosphere corrections Dual iono / bent iono Dual iono / GIM iono

  16. Altimeter parameters Ionosphere corrections (Cycle 11)

  17. Radiometer parameters Wet troposphere correction Radiometer / ECMWF Radiometer recomputed / ECMWF

  18. ENVISAT performance assessment Crossover analysis Regression coefficients at crossovers: Pseudo Time Tag Bias (ms):

  19. ENVISAT performance assessment Crossover analysis - Standard deviation (cm)

  20. ENVISAT performance assessment – crossover analysis Impact of Ionosphere corrections - Standard deviation (cm)

  21. ENVISAT performance assessment ENVISAT SLA relative to MSS* with different SSB (using Bent) * GSFC CLS01 ENVISAT SLA relative to MSS* with different iono (using BM4) ENVISAT SLA relative to MSS* with computed wet tropo using BM4 and GIM

  22. ENVISAT performance assessment Preliminary high frequency signal estimations Spectral analyses ENVISAT ERS-2

  23. ENVISAT performance assessment Preliminary high frequency signal estimations High pass filtering method Std. dev. of HF[SSH-MSS]3pts (cm) SWH (m) 6 0 5 0.5

  24. conclusions Good general performances of ENVISAT data parameter analysis crossover variance (8 cm) SLA Algorithms and corrections: need to be tuned Sea State Bias Ionosphere correction MWR correction ENVISAT bias: SSH ~ 1.26 m / MSS

  25. Cross-calibration activities brief overview Objectives: Long-term monitoring of altimeter/radiometer parameters and geophysical corrections Cross-calibration with other altimeters/radiometers ENVISAT IGDR/GDR assessment reports will include cross-calibration results This study: - ENVISAT (cycles 10 and 11) GDR ERS-2 OPR2 (from CERSAT) cycles 78 and 79 Jason 1 GDR cycles 25-36 SPTR+USO corrections Homogeneous corrections Sigma0 correction (since 01/2000) TBs drift correction (02/2003) => Wet tropo Homogeneous corrections Results presented from cycle 11 Envisat

  26. Altimeter parameters Significant Wave Height – Cross-calibration : ERS-2 Mean : 21.2 cm Standard deviation : 27 cm Slope = 0.028

  27. Altimeter parameters Significant Wave Height – Cross-calibration : ERS-2 Envisat ERS-2

  28. Altimeter parameters Significant Wave Height – Cross-calibration : Jason-1 mean 13 cm std 26 cm

  29. Altimeter parameters Significant Wave Height – Cross-calibration : Jason-1 10 days Envisat |latitude|<66° Cycle 31 Jason 1

  30. Altimeter parameters Ku-band Backscatter coefficient – Cross-calibration : ERS-2 Mean : 0.06 dB Standard deviation : 0.27 dB Slope = 0.019

  31. Altimeter parameters Ku-band Backscatter coefficient – Cross-calibration : ERS-2 ERS-2 Envisat

  32. Altimeter parameters Ku-band Backscatter coefficient – Cross-calibration : ERS-2

  33. Altimeter parameters Ku-band Backscatter coefficient – Cross-calibration : Jason 1 10 days Envisat |latitude|<66° Mean 0.61 dB Std 0.74 dB Cycle 31 Jason 1

  34. Altimeter parameters Dual Frequency ionosphere correction – Cross-calibration : Jason 1 Mean 1.5 cm Std 2 cm

  35. Radiometer parameters Cross-calibration : ERS-2 Mean 4.8 mm

  36. Radiometer parameters Cross-calibration : Jason 1 Computed Product Mean 9 mm Std 1.5 cm Mean 1.7 cm Std 1.6 cm

  37. ENVISAT performance assessment ENVISAT- ERS-2 cross-calibration (repeat-track analysis)

  38. Envisat performance assessment Envisat Jason-1 crossover SSH differences DT < 10 days / open ocean 65000 points

  39. Envisat performance assessment Envisat Jason-1 crossover SSH differences DT < 10 days / open ocean

  40. Envisat performance assessment SLA Envisat / Jason-1

  41. Cross-calibration conclusions ENVISAT bias: /ERS-2 /Jason SWH ~ 20 cm 13 cm Sigma0 ~ 0.06 dB 0.6 dB SSH ~ 1.12 m 1.05 m Wet tropo ~ 4.8 mm 1 cm SSB Dual-Frequency ionosphere Wet troposphere neural computation

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